In the art of gas metal arc welding it is common practice to use a process in which a metal wire, often referred to as a consumable electrode, is advanced through a welding gun while electrical energy is transmitted to the electrode by an electrified contact tip of the welding gun. Exemplary techniques for gas metal arc welding include MIG (Metal Inert Gas) and MAG (Metal Active Gas), with the difference between the two primarily being the type of shielding gas used. Typical inert gases are argon and helium. Typical active gases are mixtures of argon, carbon dioxide and oxygen.
In MIG/MAG-welding, the workpiece is heated primarily by an arc. The electrode is heated, partly by the power supplied when the weld current flows through the electrode and partly by the arc itself. MIG/MAG-welding takes place in one of three states. In short arc welding, the material transport from the electrode to the workpiece takes place through large short-circuiting droplets. When the supplied power is increased, the process passes into the mixed arc area, where the material transport takes place through a mixture of short-circuiting and non-short-circuiting droplets. The result is an unstable arc with significant weld spatter and weld smoke. Welding in this area is normally avoided. At a sufficiently high supplied power, the process enters the spray area, where material transport takes place through small finely dispersed droplets without short circuits. The third state is referred to as pulsed welding and means that, by means of advanced control, proper cut off of the droplets can be controlled by means of a suitable current pulse. Each pulse cuts off a droplet and the droplets become sufficiently small so as not to short-circuit. This method results in advantages from the spray area in the form of low weld spatter without the disadvantages of large heat transfer.
MIG/MAG welding electrodes are generally offered in two basic varieties: bare and coated. Both varieties can be alloyed with additional materials and provided with surface additives for enhancing performance characteristics, such as arc stability and feeding resistance. Bare electrodes, sometimes referred to as solid or uncovered electrodes, typically consist of a bare, base metal wire, such as may be formed primarily of steel, aluminum or stainless steel, that is drawn down to a desired diameter. Bare electrodes generally provide good arc start and stability between an electrode and a workpiece, as well as low feeding resistance and minimal spatter when melted. However, a problem commonly associated with bare electrodes is poor current transfer between an electrode and the contact tip of a welding gun. Current transfer instability can result in significant wear on the contact tip over a relatively short period of time, thus requiring frequent replacement of the tip. Such replacement is both inconvenient and costly.
Coated electrodes, sometimes referred to as covered electrodes, are substantially similar to bare electrodes but are provided with an exterior coating of copper, such as may be applied through conventional electroplating and electroless plating processes. The copper coating provides superior current transfer stability between the electrode and the tip of the welding gun relative to bare electrodes, thus resulting in less tip wear and less frequent tip replacement. However, coated electrodes are more costly, have greater feeding resistance, produce more spatter, and exhibit inferior arc start and arc stability between the electrode and a workpiece relative to bare electrodes. Moreover, the electroplating or electroless plating processes required for producing coated electrodes require specialized facilities and involve the use and disposal of caustic and acidic chemical agents that are harmful to the environment.